Truth be told, Ron actually liked Lavender Brown. The problem was that she seemed to like him too much. She was clingy and unbelievably jealous of every girl Ron so much as looked at. One time, he had smiled a little too brightly at Hannah Abbott after she had helped him with a Herbology question, and Lavender went on and on for hours about "overly friendly smiling" and "shows of hidden affection" that obviously meant he was replacing her. It had taken him patience he didn't even know he had to sit through the lecture. Afterwards, Harry was the poor bloke that had to listen to Ron go on and on about "paranoid, impossible-to-reason-with witches" and their "tendencies to blow everything out of proportion". And her choice of nicknames and Christmas presents? Dear Merlin, Ron didn't even want to go there.
Putting all that aside, though, Lavender definitely had redeeming traits. Years of being best friends with the Boy Who Lived made sure that he was never the one girls looked at first and gave him some very, very dangerous years of schooling. Being with Lavender changed that, you see. Her supposedly annoying clinginess actually made him feel wanted, which was something he wasn't used to at all. Sure, she might be a bit shallow and vapid, but Ron figured that was a good break from all the doom Harry brought along with his friendship.
Also, she had soft, willing lips, and her hair always felt nice when he had his fingers running through it. She smelled of her namesake flower whenever they were squashed up together in the same armchair. She showered him with affection and always cheered him on in his Quidditch matches. Hell, she even came to training sessions to watch, and sometimes brought him food she'd made for him. So, yes, if the truth was to be told, Ron actually really liked Lavender Brown.
The problem was that Ron loved Hermione. (And he bet that she had softer lips too.)